Maize DNA polymerase 2 is a phosphoprotein with increasing activity during germination

DNA replication is a late event during maize germination and DNA polymerase activity increases as germination proceeds. A replicative alpha-type DNA polymerase has been purified from maize seeds (DNA polymerase 2) and has been shown to be a multisubunit complex [Coello, P., Rodríguez, R., García, E. & Vázquez-Ramos, J. M. (1992) Plant Mol. Biol. 20, 1159-1168; Coello, P., García, E. & Vázquez-Ramos, J. M. (1994) Can. J. Botany 72, 818-822]. DNA polymerase 2 activity increased several fold during maize germination, with no apparent change in either the amount of holoenzyme or in any of the individual subunits. However, the level of phosphorylation of the 90-, 70-, 55- and 45-kDa polypeptides changed in a cyclic fashion with their highest levels occurring at 11-14 h and 45-48 h of germination. Phosphate incorporated into the different polypeptides in the 11-14-h period remained stable for at least the next 10 h (to 24 h of germination), the period of maximal enzyme activity. However, DNA polymerase 2 processivity was very similar in freshly prepared 3-h and 24-h enzymes, and no evidence was found that polymerase activity was modified by in vitro phosphorylation. The significance of these results is discussed.